1. Field of the Invention
This invention relates to locking apparatus for filter elements, and more particularly, to apparatus for releasably locking one or more filter elements into sealing engagement with a tube sheet or the like in a dust collector filter assembly.
By way of background, dust collectors of the type here comtemplated generally include a large housing divided by a tube sheet into a lower dirty air chamber and an upper clean air chamber. Several rows of cylindrical filter elements are releasably mounted in the lower chamber in sealing engagement with the lower surface of the tube sheet so that their open upper ends register respectively with corresponding openings in the tube sheet and the interiors of the elements communicate with the upper clean air chamber. More specifically, each filter element is provided with a mounting plate in the form of a flange surrounding its upper end and it is these flanges that are mounted in sealing engagement with the tube sheet, a suitable gasket being secured to each mounting plate about the open upper end of the filter elements for effecting an air tight seal with the tube sheet.
Air laden with dust particles, for example, is fed into the lower chamber and passes through the filter elements, which remove the particles from the air, and thence into tne upper chamber from which the filtered, clean air may be taken.
It is known to clean the filter elements periodically by applying downwardly directed pulses of air to the interior of each element in opposition to the direction of flow of the air being treated, thus releasing accumulated dust particles from the filter elements. The released particles accumulate in the lower chamber from which they can be removed. While this procedure of course extends the life of the filter elements, they must nevertheless be replaced from time to time.
Heretofore the filter element replacement procedure has been cumbersome, time-consuming and unpleasant and efforts have been made to provide apparatus of the class described which reduce the difficulties and time necessary to replace the filter elements. Thus, it is known from U.S. Pat. No. 4,322,231 to provide a locking arrangement by which filter elements are releasably held against the underside of the apertured tube sheet which carries pairs of locking bars, each pair supporting a row of filter elements. Each bar is semicircular in cross-section so as to define a flat supporting surface and a curved camming surface, the bars being maintained in position by a number of support brackets fixed to transverse beams depending from the tube sheet. Each bracket is formed with at least a trough within which the bars are seated and a handle is affixed to each of the bars and extends perpendicularly from the longitudinal axis of its respective bar.
When the handles are in vertical position, the underside of mounting plates associated with the filter elements, are allowed to rest on the flat surfaces of the associated locking bars so that the filter elements can slide along the bars and out of the filter housing when replacement is required.
To secure the filter elements in active position, the handles are rotated to a horizontal position causing the curved camming surfaces to bear against the underside of the mounting plates forcing the filter elements into engagement with the undersurface of the tube sheet. A gasket is secured to each mounting plate about the open upper end of the filter elements to effect a seal with the tube sheet.
Each handle is equipped with an L-shaped supporting bracket so that when an adjacent pair of locking handles are in the horizontal position, each handle may rest within the L-shaped supporting bracket of the other to prevent the handles from pivoting back to their vertical positions to release the force securing the filter element mounting plates against the tube sheet.
When it is intended to release the filter elements from active position, one of the handles is slightly raised to clear the supporting bracket of the other handle so both handles can be lowered to vertical position to rotate the locking bars and release the force securing the filter elements in active position, whereupon they may be made to slide out of the housing.
British Pat. No. 2,516,721 teaches that the filter elements are secured against the tube sheet by a tie rod extending centrally through the length of each filter and being secured at its upper end by a barrel nut received in associated notches in the upper surface of a spider secured to the lower surface of the tube sheet and centered in the associated aperture.
Attention is also invited to U.S. Pat. No. 4,323,376 disclosing a filter bag assembly insertable into the lower chamber of a housing for movement along rails into position below a flanged opening in a tube sheet between upper and lower chambers. The tube sheet supports toggle clamps that must be manually operated to raise lifting means, and thus a filter bag frame assembly, until a hook-shaped flange engages a gasket fixed to the bottom of a bulkhead to form a seal therewith.
The lifting means takes the form of an eye bolt and hex nut assembly (FIG. 7), a locking lever and hook arm (FIG. 8) or a disk secured at the lower end of a vertically movable rod (FIG. 4).
Another arrangement is disclosed in U.S. Pat. No. 4,253,856. In this case, a header plate has an aperture through which a venturi member extends to enter an end of a filter element. An annular shoulder dn the venturi member has an outer diameter at least as large as the opening and a collar having an inner diameter less than that of the outer diameter of the shoulder and surrounding the filter. The collar is releasably secured to the header plate by resilient spring steel wire clips acting through a pair of ears. These clips are coiled around pins secured to appropriate stiffening members and have a camming end that engages one ear to support the collar while the other end of the clip is releasably retained by suitable means.
A workman aligns the unit in a plate aperture and rotates the collar until flanges depending from the ears abut the pins to support the collar. Sealing of the filter unit and venturi to the tube sheet is effected by shifting the clips to place the connecting portions in holes provided for the purpose in the stiffening members.
Other relevant patents known to me are U.S. Pat. Nos. 2,641,332, 4,328,014, 4,217,122, 4,089,664, 3,083,043, 4,002,443 and 3,393,498.
It will be seen that the publications mentioned above involve complex and expensive structures and in some cases, require time consuming, manual filter element replacing operations in dust laden environments.
Moreover, none of the prior teachings known to me take into account the fact that the tube sheet with a plurality of openings required in apparatus of the class described invariably contains irregularities in its surface flatness so that if the same force is applied to each filter element when mounting it against the underside of the tube sheet, some elements will be more positively sealed than others so that leakage past the interfaces between the tube sheet and the element is a persistent problem which appears heretofore to have been neither attacked nor solved by those persons skilled in the art.